1. Field of the Invention
The present invention relates to a computer which is preferably useful as a portable or desk top computer or the like, which is relatively small in size, and which performs various scientific calculations including the four operations.
2. Description of the Related Art
Computers such as portable or desk top computers which are relatively small in size and perform various scientific calculations including the four operations are widely used. These computers are classified into several types such as a sequential calculation type, and an arithmetic expression storing type. In a sequential calculation type computer, when a number is entered and an operation key or scientific calculations key is operated, the corresponding calculation is immediately carried out. For example, immediately after a number "30" is entered and a scientific calculations, "sin" key is operated thereafter, the calculation of sin 30.degree. (sine of 30.degree.) is done and "0.5" is displayed on a display screen.
In an arithmetic expression storing type computer, when an expression to be calculated is entered and thereafter a predetermined key such as an "=" (equal) key is operated, the calculation of the entered expression is carried out. For example, by operating the "sin" key, entering a number "30" and finally operating the "=" key, the calculation of sin 30.degree. is conducted and "0.5" is displayed on a display screen.
Such a sequential calculation type computer is provided with a constant calculation function. The constant calculation is conducted as follows: an arbitrary number and an arbitrary operator are entered; the entered number is stored as a constant and the operator as an operator for the constant calculation; the constant is set (regarded) as one of a first operand and a second operand: a number entered thereafter is set (regarded) as the other of a first operand and a second operand; and the calculation corresponding the operator for the constant calculation is repeatedly carried out every time a number is entered. An example of the operations in the constant calculation in a sequential calculation type computer is shown in Table 1 below.
TABLE 1 ______________________________________ Key Operation Constant Display ______________________________________ 2 + Not set 2 3 = 2 + 5 4 = 2 + 6 ______________________________________
At first, "2" and "+" are entered, and "2" is displayed on a display screen. Then, when "3" and "=" are entered, "2" is set as a first operand, "+" is set as the operator for the constant calculation, and newly entered "3" is set as a second operand; the calculation between the first operand and the second operand (in this example, the addition) is carried out; and "5" is displayed on the display screen.
When "4" and "=" are entered thereafter. "2" is set as the first operand in the same manner as described above, and entered "4" is set as the second operand. The calculation between the first operand and the second operand (in this example, the addition) is carried out, and "6" is displayed on the display screen.
Generally, an arithmetic expression storing type computer is not provided with such a constant calculation function.
Recently, arithmetic expression storing type computers such as so-called pocket computers having a calculation function enhanced to be higher than that of an arithmetic expression storing type computer are popularly used. In such a pocket computer, a program (calculation procedure) which corresponds to a program language such as BASIC and FORTRAN for a usual computer can be input and executed.
In order to set the constant calculation function, such a pocket computer is provided with a special key called "CONST" key. An example of the operations in the constant calculation in a pocket computer is shown in Table 2 below.
TABLE 2 ______________________________________ Key Operation Constant Display Indication Sign ______________________________________ 2 + Not set 2+- CONST 2 + &gt; CONST 3 2 + 3- CONST ENTER 2 + 5 CONST 4 ENTER 2 + 6 CONST ______________________________________
Firstly, "2" and "+" are entered, and "2+" is displayed on a display screen, further a cursor which indicate an input position is displayed in the digit subsequent to that of "+". When the "CONST" key is operated under this state, the constant calculation mode is set, and a prompt sign, "&gt;" is displayed on the display screen to request the user to conduct a further key entry. At this time, "2" is set as a first operand, and "+" as the operator for the constant calculation. On the display screen, "CONST" is displayed as an indication sign. In this pocket computer, an indication sign denotes the current operation mode of the pocket computer and is kept displayed till the operation mode is canceled. Namely, the indication sign "CONST" is kept displayed till the constant calculation mode is canceled.
When "3" is entered in sequence, "3" is displayed on the display screen and a cursor is displayed in the digit subsequent to that of "3". When an "ENTER" key is then operated to indicate the completion of the entry of a numeric and the initiation of the calculation, "3" is set as a second operand, and the calculation of "2+3" is carried out and the calculation result of "5" is displayed.
When "4" is entered and the "ENTER" key is then operated, "4" is set as a second operand, and the calculation of "2+4" is carried out and the calculation result of "6" is displayed.
In the pocket computer, for example, when ".div." and "2" are entered and the "CONST" key is operated, the constant calculation mode in which "2" is set as a second operand and ".div." as the operator for the constant calculation is set.
The constant calculation function of the sequential calculation type computer is restricted to a calculation in which the initially entered number is treated as an first operand, and cannot perform a constant calculation of another kind in which the initially entered number is set as a second operand and a number entered in later as an first operand.
As described above, an arithmetic expression storing type computer is not provided with a constant calculation function.
In order to execute a constant calculation function, such a pocket computer must be provided with the "CONST" key. This causes a problem in that the number of keys is increased. Moreover, it is required to display "CONST" as an indication sign, the display screen must include a display area for displaying the indication sign "CONST".